Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. Also, the secondary battery has attracted considerable attention as a power source for electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (Plug-in REV), which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuels.
Small-sized mobile devices use one or several battery cells for each device. On the other hand, middle or large-sized devices, such as vehicles, use a middle or large-sized battery module having a plurality of battery cells electrically connected to one another because high power and large capacity are necessary for the middle or large-sized devices.
Preferably, the middle or large-sized battery module is manufactured so as to have as small a size and weight as possible. For this reason, a prismatic battery or a pouch-shaped battery, which can be stacked with high integration and has a small weight to capacity ratio, is usually used as a battery cell of the middle or large-sized battery module. In particular, much interest is currently focused on the pouch-shaped battery, which uses an aluminum laminate sheet as a sheathing member, because the pouch-shaped battery is lightweight, the manufacturing costs of the pouch-shaped battery are low, and it is easy to modify the shape of the pouch-shaped battery.
In order for the middle or large-sized battery module to provide power and capacity required by a predetermined apparatus or device, it is necessary for the middle or large-sized battery module to be configured to have a structure in which a plurality of battery cells are electrically connected in series to each other, and the battery cells can suitable resist external force.
Also, the battery cells constituting the middle or large-sized battery module are secondary batteries which can be charged and discharged. Consequently, a large amount of heat is generated from the high-power, large-capacity secondary batteries during the charge and discharge of the batteries. If the heat, generated from the battery cells during the charge and discharge of the battery cells, is not effectively removed, the heat accumulates in the battery cells, with the result that deterioration of the battery cells is accelerated. According to circumstances, the battery cells may catch fire or explode. For this reason, a cooling system is needed in a battery pack for vehicles, which is a high-power, large-capacity battery, to cool battery cells mounted in the battery pack.
In a middle or large-sized battery pack including a plurality of battery cells, on the other hand, the deterioration in performance of some battery cells leads to the deterioration in performance of the entire battery pack. One of the main factors causing the nonuniformity of the performance is nonuniform cooling between the battery cells. For this reason, it is necessary to provide a structure in which the shape of a coolant flow channel is optimized to minimize temperature deviation between the battery cells during the flow of a coolant.
Some conventional middle or large-sized battery packs use a battery pack case configured to have a structure in which a coolant inlet port and a coolant outlet port are disposed at the upper part and the lower part of the battery pack case so that the coolant inlet port and a coolant outlet port face in opposite directions, and the top and bottom of a flow space extending from the coolant inlet port to the battery module are parallel to each other. In this structure, however, a relatively high coolant flux is introduced into coolant flow channels defined between the battery cells adjacent to the coolant outlet port, whereas a relatively low coolant flux is introduced into coolant flow channels defined between the battery cells adjacent to the coolant inlet port, with the result that temperature deviation between the battery cells is high.
In connection with this matter, Korean Patent Application Publication No. 2006-0037600, No. 2006-0037601, and No. 2006-0037627 disclose a middle or large-sized battery pack configured to have a structure in which an air guide plane is inclined downward to a side opposite to battery cells so that the air guide plane becomes closer to the battery cells with the increase in distance between the air guide plane and a coolant inlet port. Specifically, the air guide plane is inclined at an angle of 15 to 45 degrees to the side opposite to the battery cells and the coolant inlet port is formed in parallel, thereby restraining the occurrence of a phenomenon in which coolant flux is excessively introduced into coolant flow channels defined between the battery cells adjacent to the coolant outlet port.
However, the inventors of the present application have found that, in a case in which the coolant inlet port is disposed higher than the pack case, i.e. for a middle or large-sized battery pack including a pack case configured so that the inclination of the coolant inlet port is greater than the inclination of the end opposite to the coolant inlet port in consideration of a device in which the pack case is installed, it is not possible to restrain the occurrence of a phenomenon in which coolant flux is excessively introduced into the coolant flow channels defined between the battery cells adjacent to the coolant outlet port when the inclination angle of the air guide plane is 15 to 45 degrees as described above with the result that the temperature deviation between the battery cells is increased, and therefore, it is not possible to achieve a desired level of cooling uniformity.
Consequently, there is a high necessity for a technology to fundamentally solve the above-mentioned problems.